[LSF/MM TOPIC][LSF/MM ATTEND] NAPI polling for block drivers

[Sagi Grimberg]

>     So it looks like we are super not efficient because most of the
>     times we catch 1
>     completion per interrupt and the whole point is that we need to find
>     more! This fio
>     is single threaded with QD=32 so I'd expect that we be somewhere in
>     8-31 almost all
>     the time... I also tried QD=1024, histogram is still the same.
>
>
> It looks like it takes you longer to submit an I/O than to service an
> interrupt,

Well, with irq-poll we do practically nothing in the interrupt handler,
only schedule irq-poll. Note that the latency measures are only from
the point the interrupt arrives and the point we actually service it
by polling for completions.

> so increasing queue depth in the singe-threaded case doesn't
> make much difference. You might want to try multiple threads per core
> with QD, say, 32

This is how I ran, QD=32.